1. Field of the Invention
The present invention relates to a process for evaluating microbial-degradability of organic matters and an apparatus employed therefor, particularly to a process and an apparatus for evaluating microbial-degradability of biodegradable plastics, organic industrial waste including hardly degradable organic matters such as PCB and other organic matters.
2. Earlier Technologies
Environmental disruption brought about by industrial waste is now of a global concern. That is, pollution of soil and pollution of ocean to be caused by damping industrial waste into the soil or at the sea can be causative of disruption of ecosystem including the human society, giving rise to a serious social problem. Under such circumstances, degradation of organic waste to be achieved by microorganisms is the cleanest purification system that occurs in the realm of nature. Accordingly, to substitute those substances which are now chemically synthesized with those having microbial-degradability can be a useful measure for solving or improving the problem of environmental disruption induced by industrial waste as described above.
As an example of such substance having microbial degradability, biodegradable plastics which are decomposed by soil or water microorganisms are under development and are sharing some part of organic industrial waste. The biodegradable plastics are expected:
(1) to be stable during the period of use, and PA1 (2) to be decomposed soon in the soil by microorganisms after disposal. PA1 (1) quantitative determination of carbon dioxide captured in a strong alkaline solution by means of neutralization titration; and PA1 (2) quantitative determination of carbon dioxide captured in a gas reservoir by use of a gas analyzer. PA1 (a) a method in which biodegradable plastic samples are buried in various kinds of soils to allow them to be decomposed by soil microorganisms for a predetermined period. After this period, the biodegradable plastics are dug out of the soils, and their states are compared with those before they were buried; and PA1 (b) a method in which biodegradable plastics are allowed to be decomposed by activated sewage sludge microorganisms to measure the amount of carbon dioxide formed by decomposition by means of titration. This method is stipulated under ASTM (American Society for Testing and Materials D5209-92, D5338-92). PA1 taking an organic matter as an evaluation subject together with a prescribed microbial source into a reaction column maintained constantly at a fixed temperature to effect decomposition of the organic matter in the reaction column by microorganisms contained in the prescribed microbial source under feeding of CO.sub.2 -free saturated water vapor into the reaction column and to measure the weight of carbon dioxide formed by the decomposition; PA1 taking a cellulose as a evaluation reference together with the same prescribed microbial source as described above into another reaction column maintained constantly at the same fixed temperature as described above to effect decomposition of the cellulose in the reaction column by the microorganisms contained in the prescribed microbial source under feeding of CO.sub.2 -free saturated water vapor into the reaction column and to measure the weight of carbon dioxide formed by the decomposition; and PA1 carrying out comparative discussion of these two measured values so as to evaluate degradability of the organic matter.
Although it is possible to measure the period during which biodegradable plastics can be used stably, there is established no standardized means of measuring the rate of degradation in biodegradable plastics to be caused by microorganisms, so that evaluation results of biodegradable plastics are of inconsistency, which is a main cause of hindering development of high-quality biodegradable plastics.
There exists so far no evaluation apparatus relating to total degradation of organic matters in the soil and in compost into carbon dioxide (carbonic acid gas). As carbon dioxide analytical methods, the following methods are generally known:
However, since the volume or weight of the organic matter to be tested ranges widely from 1 cc to several hundreds of tons, and besides organic matters are of different compositions, there is reported no standardized test method. Accordingly, the test method (1) or (2) is selected depending on the respective subjects to be tested, with no established standardized means for evaluating biodegradability.
However, the conventional methods for evaluating biodegradability of biodegradable plastics involve the following problems respectively.
Method (a)
This method includes indeterminate factors: variation in the kinds and numbers of inhabitant microorganisms depending on the soil in which biodegradable plastics are buried and variation in the natural conditions including temperature, rains, etc. In other words, the conditions under which the samples are decomposed by microorganisms vary greatly depending on the soil. Accordingly, evaluation of biodegradability in biodegradable plastics carried out for various kinds of soils brings about inconsistent results. That is, evaluation of biodegradability obtained according to the method (a) is of low reliability.
Method (b)
This method requires a long-term maintenance of instruments and devices and an experienced technician, because the amount of carbon dioxide formed during decomposition is adapted to be determined by titration. Further, while this method employs activated sewage water sludge from a municipal waste water treatment tank as a microbial source, it involves a problem in that the rate of decomposition to be achieved by microorganisms varies depending on the sludge employed, since the kinds and numbers of inhabitant microorganisms which achieve decomposition of biodegradable plastics vary depending on the soil employed. In other words, the measured values of biodegradability evaluation include significant errors due to the indeterminate factors in that the kinds and numbers of inhabitant microorganisms which achieve decomposition of biodegradable plastics vary depending on the sludge employed.